CROP MONITOR

Oilseed Rape National Report, 20 June 2005

Monitoring is carried out on a monthly basis from mid December

This report was prepared by Peter Gladders, ADAS

Overview:

Forward crops are starting to ripen and have seeds that are brown -green mottled (GS 6,4), most still have green seeds (GS 6,3) and only a few late crops still have translucent seeds. Crop canopies are leaning or lodging in the more vigorous crops. There are signs of premature ripening where phoma stem canker has not been controlled. Few observers inspect crops regularly in June, but early indications suggest sclerotinia and alternaria levels are low. Alternaria could still increase if thunderstorms continue. Powdery mildew is increasing on leaves, pods and stems and will continue to increase whilst crops are green. Light leaf spot is obvious on stems and pods in a few crops.

North:

Most crops are at the green seed stage with a few showing green-brown seeds (GS 6,3-6,4).

At the reference monitoring site on the Wolds, the crop had fungicide sprays in October and late November. These have given good control of phoma stem canker which affected 72% untreated plants and 28% of treated plants. The incidence of moderate and severe cankers that are likely to reduce yield was 24% inuntreated areas and 4% in the treated area.
Light leaf spot has become more severe over the last two months and has started to affect the pods in a few crops. The refrence crop has obvious stem lesions of light leaf spot and about 70% control was achieved with autumn fungicides. Sclerotinia and alternaria levels appear to be generally low, but could increase further given crop lodging and continuing wet weather.

East:

Most crops are at the green seed stage with a few showing green-brown seeds (GS 6,3-6,4). The crop monitored at Terrington received its fungicide on 6 December and is showing very high levels of phoma stem canker in both treated and untreated areas. Some lesions have already affected more than half the stem circumference and will cause premature ripening. Fungicide timing was rather late at this site and control with this single spray is poor. Stem canker lesions are slightly less severe where fungicide was used compared with untreated lesions which are starting to weaken the stem. Yield loss from stem canker is expected this season. Fungicides have given good control of phoma stem canker in replicated experiments this season. If canker is causing prematurely ripened plants in the crop by early July, poor spray timing may be responsible.
Sclerotinia activity is generally low this season and most crops have less than 1% plants are affected in reports so far. Alternaria is present at low levels, occasionally affecting the pods. Powdery mildew is the most obvious disease on pods and stems in some crops.

West:

Most crops are at the green seed stage with a few showing green-brown seeds (GS 6,3-6,4).
At the Wolverhampton reference site, phoma leaf spot has fluctuated quite markedly this season (more so than in other crops), but stem cankers are now present on 44% of untreated plants. Most of the stem cankers are small lesions and only a few have girdled more than 50% stem circumference.
Sclerotinia activity is generally low this season and most crops have less than 1% plants are affected in reports so far. Alternaria is present at low levels, occasionally affecting the pods. Powdery mildew appears to be rather less prevalent than in the east.

South East:

Most crops are at the green seed stage with a few showing green-brown seeds (GS 6,3-6,4).
Phoma stem cankers have developed in the untreated reference crop to affect 76% of plants,with symptoms ranging from moderate to severe. The fungicide treated crop has 60% plants with stem canker, many of which are moderately severe and likely to reduce yield. Both alternaria and powdery mildew are building up in the crop. Light leaf spot activity has remained low in the region and pod infection is limited. Sclerotinia is being reported in the region and untreated crops in high risk situations may have up to 10% plants affected.

South West:

Most crops are at the green seed to green-brown seed stage (GS 6,3-6,4).
The reference crop is in a lower disease risk area in Devon but phoma stem cankers have affected 36% of untreated plants compared with 8% after fungicide applied on 26 November. Phoma stem lesions are also common in this crop. Light leaf spot has increased again and affects stems of 76% of untreated plants and 32% of treated plants. The large black lesions are superficial and affected up to 25% of stem area. There are low levels of alternaria and light leaf spot on the pods of most untreated plants. Alternaria can increase rapidly if the weather is hot and showery. Sclerotinia levels are generally low. control are now largely complete.

Decisions:

Review the disease situation on a field by field basis before swathing or desiccation and identify causes of premature ripening or pod shattering. Plan cropping for autumn and adjust mangement requirements in the light of 2004/05 season.

Select varieties with good resistance to phoma stem canker and light leaf spot for sowing in autumn 2005.

Plan cultivation or ploughing of oilseed rapestubbles to reduce spread of air-borne fungal spores to new crops.

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